It got it back once they had a computer (PCM) fast enough.

 

If you find the technology interesting look at how the Rover VVC engine works; it certainly confused me when I had to change 2x timing belts on Mrs la_guillotine's MGF.

Touch wood I have never had any issues for any type of variable valve timing on my cars, but I have had problems with air flow control and ERGs. I also remember how rough my friends 80's cars were at low revs after they changed the cam shafts for performance ones.

Overall I consider it an efficiency technology (like, overhead cams, 4 valves per cylinder etc..) rather than an emission control technology (like ERGs, cats etc...)

 

Thanks so much for the info and link. I do indeed have the AJ27 motor with the continuously variable valve timing in my 2001 XK8. And the link is a great source of detail. The VVT algorithm is quite simple. It's based on RPM and engine load. Page 9.2 is the start of the description.
I've been poking around and Alfa Romeo had the first production VVT way back in 1980. It was just based on RPM, advancing the cam around 2000 and de-advancing it around 5000.
https://en.wikipedia.org/wiki/Variat..._valve_timing)
I'm a happy camper today. We engineers don't need much to make us happy, just how everything works and why!

 

The VVT unit in the AJ26 Engine guide is the early binary on/off type.
These look different plane on the outside no ribs (see picture below).
On these solenoid only lets oil in or not.
I think most people have later AJ26's with variable VVT units.
This needs a more complex solenoid and control system.
Assume this controls the oil pressure/flow and then amount of advance.
This system is not shown in the AJ26 Engine guide (see picture below).
I thinks this explains some confusion about the solenoid valves.




Binary VVT without retard holes (only on or off)